The CORE Group Polio Project (CGPP) and its partners in India, Angola, and Ethiopia have led successful social mobilization efforts to reach difficult-to-access populations critical for polio eradication.These include extremely poor rural and urban communities, ethnic and religious minorities who resist immunizing their children, and others such as newborns, pastoralists, migrants, and those in transit across national borders. Working through grassroots nongovernmental organizations (NGOs) including religious leaders, CGPP social mobilization activities have contributed to the current polio-free status in all three countries and have improved the coverage of children’s routine immunizations as well. Marking a shift from the earlier dominance of epidemiological perspectives, today behavior-change communication —advocacy, interpersonal communication, and social mobilization — is recognized internationally as the way forward in this final phase of polio eradication.